The present invention relates to a process for electrochemical oxidation of bromide to bromine. The present invention more particularly relates to oxidation of bromide ions in brine, bittern and effluents using an indigenous cation exchange membrane flow cell.
Oxidation of bromide in its source produces the elemental bromine, which is primarily used in the manufacture of both organic and inorganic bromo compounds. The compounds of bromine are well represented in many areas such as gasoline additives, agricultural chemicals, flame-retardants, dyes, photographic chemicals, pharmaceuticals etc. Besides, the high-density organo bromine compounds as hydraulic, gear/ore flotation fluids, the CaBr2-ZaBr2 composition as drilling fluid and the 1,2-dibromo ethylene as anti-knocking agent in gasoline are known to be useful. In addition, bromine is directly used as disinfectant in swimming pools, and as anti oxidant to control the growth of bacteria, algae and odor in cooling waters. It is also used for desizing of cotton, bleaching of pulp and paper, and in laboratories as a reagent.
Reference may be made to A. Frank (Z. E. Jolles, Bromine and its Compounds, Ernest Benn Limited, London 1966) wherein the oxidation of bromide to bromine has been reported by using manganese dioxide in sulfuric acid medium at 60xc2x0 C. The main drawbacks of this process are that the use of sulfuric acid is hazardous, gives insoluble calcium sulfate leading to the clogging of various parts of the equipment and needs extra precautions or steps in using it. Moreover, the bromine yields are very low.
D. Callihan and E. O. Salant in J. Chem. Phys. 1934, 2, 317 have used alkali chlorate salts in place of manganese dioxide to oxidize bromide ion to bromine. The drawbacks of this method are that the oxidant is costly and it requires a mineral acid like sulfuric or hydrochloric additionally. Moreover, the chlorate salts are known to be explosive. The possibility of formation of calcium sulfate precipitate particularly when sulfuric acid is used, may lead to the blocking of various parts of the equipment.
S. M. Naude and H. Verleger Proc. Phys. Soc. 1950, 63A, 470 has used chlorine gas in place of manganese dioxide and alkali chlorates to oxidize bromide to bromine in acidic solutions. The problems normally faced with this are the handling of the more corrosive chlorine gas and the difficulty in its transportation which effects the cost.
According to Wunsche process, D. F. Homig and W. E. Osberg in J. Chem. Phys. 1955, 23, 662, have used a two compartment cell consisting of a pair of graphite electrodes for the oxidation of bromide containing sea waters. In this method, a porous clay sheet was used as the diaphragm between the electrodes for better current efficiency. The cell was operated at 11.5 mA/cm2 against a cell potential of 3-4 V. The main disadvantages of this process are that the pores of the clay diaphragm get clogged by the insoluble magnesium hydroxide produced at the cathode compartment and hence reduce the process efficiency.
A. Anderson et al. in Phil. Mag. 1962, 7, 1243 have disclosed another Kossuth process wherein a simple electrochemical cell having bipolar carbon electrodes was employed without any diaphragm. In this cell, the cathode and the anode plates were mounted on a non-conductive plate of equal size in such a way that the exposed surfaces can carry the electrolysis process. The magnesium hydroxide precipitated on the cathode was dislodged by reversing the polarity of the electrodes and subsequently removed from the brominated solution by filtration before it was sent to a stripping column. The disadvantage of this method is that it requires additional device to reverse the polarity of the electrodes and increase one unit operation of filtration of magnesium hydroxide before sending to a bromine-stripping column, which are cumbersome and not economically viable. This process is inferior due to its low current (40-50%) efficiency.
More recently, Sumitomo Chemical Co. Ltd., Jpn. (JP 60 54,905; 29 Mar. 1985) have claimed the continuous manufacture of bromine and its steam distillation wherein the aqueous solutions of hydrobromic acid and sodium bromide were oxidized with chlorine gas. The drawback of this method requires handling of hazardous chlorine and is adaptable to low volumes. Moreover, the method requires acidifying the bromide solutions with a mineral acid.
T. Jakagi, S. Sigeo and S. Matsuoka from Toatsu Chemicals, Inc., Jpn. (JP 63 203,781, 23 Aug. 1988) have prepared a saturated solution of bromide containing raw salt and electrolyzed in an anode chamber of an ion-exchanger type cell under a slight application of pressure to concentrate bromine in the returned salt water. The drawbacks of this method are that it does not work in the presence of calcium and magnesium salts. Moreover, it requires pressuring the solution for concentrating the bromine.
N. Ogawa et al. from Tosoh Corp. Jpn. (JP 04,170,302, 18 Jan. 1992) have patented the manufacture of bromine by the oxidation of bromide in bromine containing salt solutions employing chlorine gas at pHxe2x89xa64 and the freed bromine was separated with air in glass-bed packed columns. The drawbacks of this method are that it requires acidification of the salt solutions and also requires the handling of hazardous chlorine to oxidize bromide.
P. Schubert et al. in Catalytica, Inc. PCT Int. Appl. WO 9,306,039, 1 Apr. 1993, have disclosed a catalytic process for oxidizing bromine from alkali/alkaline earth metal bromide salts. In this process the source material is acidified to produce gaseous hydrobromic acid thereby oxidizing the bromide by oxygen over a metal oxide catalyst to produce a stream of bromine and water vapor. The drawbacks of this process are that it needs acidification and heating steps involving a catalyst, which adds to the production cost of bromine.
R. C. Williams et al. in U.S. Pat. No. 5,254,226, 19 Oct. 1993, have described an automatically operated electrolytic cell assembly and a method of efficiently providing brominated water using bipolar graphite electrodes. The drawbacks of this method are that it requires a mechanical devise to monitor the power on and off at a selected time and intermittently the polarity of the electrodes has to be reversed to clean the electrodes to prevent the formation of hydrolyzed products and subsequent clogging.
M. Jean-Charles et al. (PCT Int. Appl. WO 9,600,696, 11 Jan. 1996, 19pp. Fr) have revealed an apparatus working at high temperature and pressure for bromine recovery from liquid effluents. The combustion gases were cooled and subjected to hetero-azeotropic distillation to obtain the gaseous water-bromine mixture. The bromine was decanted at around 5xc2x0 C. and distilled to get a purity of 99.9%. The main drawback of this method is that it involves energy intensive steps like combustion at high temperature and pressure and hetero-azeotropic distillation, which unnecessarily adds to the production cost.
M. Yamada et al. in the patent Kokai Tokkyo Koho JP 07,171,581, 11 Jul. 1995, have processed the photographic wastewaters for the recovery of bromine. It comprises the separation and recovery of bromine by spray incineration of photographic wastewater with alkali metal hydroxides, carbonate salts, nitrate salts and/or organic acid salts under oxidative atmosphere. Chlorine gas or hypochlorous acid was used to free the bromine in the incinerated water solution. The main drawbacks of this method are that it involves energy intensive steps like incineration with alkali metal hydroxides, carbonate salts, nitrate salts and/or organic acid salts under oxidative atmosphere and requires an additional oxidation step, which is uneconomical. Further, it needs handling of hazardous chlorine gas/hypochlorous acid.
The main object of the present invention is to provide a process for electrochemical oxidation of bromide to bromine in brine, bittern and effluents using a cation exchange membrane flow cell which obviates the drawbacks as detailed above.
An object of the present invention is to use an indigenous cation ion-exchange membrane in a two compartmental solid polymer electrolyte flow cell.
Yet another object of the present invention is to use precious triple metal oxide coated titanium as stable catalytic anode to oxidize bromide to bromine.
Still another object of the present invention is to oxidize inorganic bromide present in non-acidified brine, bittern or enriched effluents to bromine.
Further object of the present invention is to prevent clogging caused by the formation of insoluble sulfates or hydroxides of magnesium and calcium at the cathode.
Still another object of the present invention is to achieve the oxidation of 5 to 80% bromide to bromine under single pass conditions with 30 to 1000% coulombic efficiency.
The present provides a process for electrochemical oxidation of bromide to bromine. The present invention more particularly relates to oxidation of bromide ions in brine, bittern and effluents using an indigenous cation exchange membrane flow cell.